1. Field of the Invention
The present invention deals with the field of electrical devices generally known as relays as well as the control circuit operative therewith. Such relay devices normally include a coil with relay contacts which are operable to close and open responsive to powering and de-powering, respectively, of the coil. This is an electro-mechanical operation which normally occurs in a matter of milliseconds. However, immediately after opening of the mechanical contacts, transient arcing currents can occur which tend to damage the surfaces of the mechanical contact by burning or allowing material to migrate from one contact to the other. Some minor arcing may also occur immediately after closing of the mechanical contacts if they bounce or wipe with respect to one another. Devices have been designed for the purposes of minimizing these transient arcing currents, however, the present invention provides a very rapidly responsive transient current suppressing system which preferably makes use of optical coupling and can be utilized with AC or DC relay coils.
2. Description of the Prior Art
Numerous prior art patents have been found for the purposes of relay control and the suppression of arcing in cross relay contacts such as shown in U.S. Pat. No. 2,637,769 patented May 5, 1953 to A. H. B. Walker and assigned to Westinghouse Brake and Signal Company Limited on a xe2x80x9cMeans For Suppressing Arcing at Contacts Breaking A Direct Current Inductive Circuitxe2x80x9d; and U.S. Pat. No. 3,372,303 patented Mar. 5, 1968 to L. G. W. Knott and assigned to F. Devetta (Electronics) Limited on xe2x80x9cA. C. Switch Contactsxe2x80x9d; and U.S. Pat. No. 3,555,353 patented Jan. 12, 1971 to Charles F. Casson and assigned to American Machine and Foundry Company on a xe2x80x9cMeans Effecting Relay Contact Arc Suppression In Relay Controlled Alternating Load Circuitsxe2x80x9d; and U.S. Pat. No. 3,558,910 patented Jan. 26, 1971 to Robert G. Dale et al and assigned to Motorola, Inc. on xe2x80x9cRelay Circuits Employing A Triac To Prevent Arcingxe2x80x9d; and U.S. Pat. No. 3,639,808 patented Feb. 1, 1972 to Gerald R. Ritzow and assigned to Cutler-Hammer, Inc. on xe2x80x9cRelay Contact Protecting Circuitsxe2x80x9d; and U.S. Pat. No. 3,783,305 patented Jan. 1, 1974 to Peter Lefferts and assigned to Heinemann Electric Company on an xe2x80x9cArc Elimination Circuitxe2x80x9d; and U.S. Pat. No. 3,982,137 patented Sep. 21, 1976 to John K. Penrod and assigned to Power Management Corporation on an xe2x80x9cArc Suppressor Circuitxe2x80x9d; and U.S. Pat. No. 4,025,820 patented May 24, 1977 to John K. Penrod and assigned to Power Management Corporation on a xe2x80x9cContactor Device Including Arc Suppression Meansxe2x80x9d; and U.S. Pat. No. 4,152,634 patented May 1, 1979 to John K. Penrod and assigned to Power Management Corporation on a xe2x80x9cPower Contactor And Control Circuit; and U.S. Pat. No. 4,251,845 patented Feb. 17, 1981 to Harold E. Hancock and assigned to Power Management Corporation on an xe2x80x9cArc Suppressor Circuitxe2x80x9d; and U.S. Pat. No. 4,296,449 patented Oct. 20, 1981 to Charles W. Eidhelberger and assigned to General Electric Company on a xe2x80x9cRelay Switching Apparatusxe2x80x9d; and U.S. Pat. No. 4,360,847 patented Nov. 23, 1982 to Milton D. Bloomer et al and assigned to General Electric Company on a xe2x80x9cDiode Assisted Relay Contactorxe2x80x9d; and U.S. Pat. No. 4,389,691 patented Jun. 21, 1983 to Harold E. Hancock and assigned to Power Management Corporation on a xe2x80x9cSolid State Arc Suppression Devicexe2x80x9d; and U.S. Pat. No. 4,438,472 patented Mar. 20, 1984 to George K. Woodworth and assigned to IBM Corporation on an xe2x80x9cActive Arc Suppression For Switching Ofg Direct Current Circuitsxe2x80x9d; and U.S. Pat. No. 4,525,762 patented Jun. 25, 1985 to Claude R. Norris on an xe2x80x9cArc Suppression Device and Methodxe2x80x9d; and U.S. Pat. No. 4,700,256 patented Oct. 13, 1987 to Edward K. Howell and assigned to General Electric Company on a xe2x80x9cSolid State Current Limiting Circuit Interrupterxe2x80x9d; and U.S. Pat. No. 4,745,511 patented May 17, 1988 to Michael M. Kugelman et al and assigned to The BF Goodrich Company on a xe2x80x9cMeans For Arc Suppression In Relay Contactsxe2x80x9d; and U.S. Pat. No. 4,754,360 patented Jun. 28, 1988 to Ryosaku Nakada and assigned to Nipponkouatsudenki Kabushikikaisha on an xe2x80x9cArc Extinguishing Apparatus Having Sensing of Initial Arcxe2x80x9d; and U.S. Pat. No. 4,760,483 patented Jul. 26, 1988 to Michael M. Kugelman et al and assigned to The B.F. Goodrich Company on a xe2x80x9cMethod For Arc Suppression In Relay Contactsxe2x80x9d; and U.S. Pat. No. 4,772,809 patented Sep. 20, 1988 to Hirofumi Koga et al and assigned to Omron Tateisi Electronics Co. on a xe2x80x9cSwitching Circuit And A Relay Device Employed To Prevent Arcingxe2x80x9d; and U.S. Pat. No. 4,816,818 patented Mar. 28, 1989 to Philip C. Roller and assigned to Truck-Lite Co., Inc. on a xe2x80x9cHeavy Duty Lamp Flasher For Trucks, Trailers And The Likexe2x80x9d; and U.S. Pat. No. 4,855,612 patented Aug. 8, 1989 to Hirofumi Koga et al and assigned to Omron Tateisi Electronics Co. on a xe2x80x9cSwitching Current And A Relay Device Employed Thereinxe2x80x9d; and U.S. Pat. No. 4,959,746 patented Sep. 25, 1990 to Chester C. Hongel and assigned to Electronic Specialty Corporation on a xe2x80x9cRelay Contact Protective Circuitxe2x80x9d; and U.S. Pat. No. 5,081,558 patented Jan. 14, 1992 to Leo M. Mahler and assigned to Northrop Corporation on xe2x80x9cHigh Voltage DC Relaysxe2x80x9d; and U.S. Pat. No. 5,247,418 patented Sep. 21, 1993 to George C. Auge on an xe2x80x9cArc Suppressing Switchxe2x80x9d; and U.S. Pat. No. 5,536,980 patented Jul. 16, 1996 to Keith W. Kawate et al and assigned to Texas Instruments Incorporated on a xe2x80x9cHigh Voltage, High Current Switching Apparatusxe2x80x9d.
The present invention takes advantage of the useful characteristics of a mechanical relay in combination with the advantages of a solid state relay by combining operation therebetween. In particular, the mechanical relay has contacts which can carry higher currents for longer periods of time without deterioration and without any need for dissipating heat. This characteristic is apparent in mechanical contacts since the current flowing therethrough generates a negligible amount of heat because of the very low voltage drop across these contacts when fully closed. The disadvantage, however, of mechanical contacts within the mechanical relay is that damaging arcing often occurs, immediately after opening, because at these times the contacts are very close to one another and arcing can easily occur. This arcing causes appreciable erosion of the contacts and deteriorates the contact surfaces and undesirably increases the voltage drop across such contacts, and can ultimately lead to contact failure. The deterioration of the mechanical contact surfaces can be attributable to the migration of material which can occur during the arcing, as well as the burning or charring of the contact surfaces.
A solid state switching mechanism has strikingly different operating characteristic advantages and disadvantages. In particular, a solid state switch such as a thyristor or transistor can open or close electrical circuits without any arcing whatsoever because of the nature of the solid state design. The problem with these devices however is they are severely stressed or can be permanently damaged by heat which builds up quickly when required to carry high currents. This unwanted heat is the result of the high voltage drop across these devices during operation thereof. Thus, very large and somewhat expensive heat sinks or other heat dissipation devices must be used in order to remove the heat when such solid state switches are required to carry fairly large currents for long periods of time.
The present invention takes advantage of the distinctively different characteristics of the mechanical relay and the solid state switch by using circuitry that connects the solid state switch in parallel to the relay contact. In the configuration of the present invention the solid state switch is operative to begin conducting, that is, becomes turned on just before the relay contacts close and become non-conductive a short time after the relay contacts have opened and remain non-conductive outside of these time periods. However, once the mechanical contacts are closed, since the voltage drop across the mechanical contacts is much lower than the voltage drop across the solid state switch, almost all current will flow through the mechanical switch thereby having virtually no current flow through the solid state-switch even though the switch is technically xe2x80x9conxe2x80x9d. This is because the solid state switch has such a higher voltage drop there across which almost eliminates current flow therethrough and thus the switch acts as if it were not capable of operating.
To achieve this configuration the present invention preferably includes a relay which includes relay contacts which are movable between an open position preventing current flow therethrough and a closed position allowing current flow therethrough. A relay coil is included also which is electromagnetically operatively connected to the relay contacts and is operative to urge the relay contacts to the closed position responsive to powering of the relay coil and is operative to allow movement of the relay contacts to the open position responsive to de-powering of the relay coil. A relay coil powering circuit is also included electrically in series with the relay coil for selectively powering and de-powering thereof. This relay coil powering circuit can be AC powered or DC powered.
An arc suppression circuit is included as a critical aspect of the present invention which senses the powering and de-powering of the relay coil. This arc suppression circuit is designed for suppressing transient electrical arcing across the relay contacts during closing and opening thereof. The arc suppression circuitry preferably includes a first solid state circuit in electrical communication with the relay coil powering circuit to be activated selectively responsive to powering and de-powering of the relay coil. This first solid state circuit is electrically in parallel with respect to the relay coil. The apparatus further includes a second solid state circuit means which is electrically coupled to the first solid state circuit to sense activation and termination thereof. This coupling is preferably made through an electromagnetic coupling means such as an optocoupler. The second solid state circuit is connected electrically in parallel with respect to the relay contact to prevent arcing therebetween by shunting thereover.
The configuration of the first solid state circuit preferably includes a first diode in series with the electromagnetic coupling means in order to maintain current flow therethrough in only one direction. A current limiting resistor is also included in series with the first diode positioned between the electromagnetic coupling means and the first diode to limit current flow therethrough and control delays. A primary capacitor is also included electrically in parallel with respect to the current limiting resistor. This primary capacitor is adapted to discharge through the current limiting resistor and the optocoupler for a limited period of time responsive to de-powering of the first solid state conduit means in order to activate the second solid state circuit and eliminate transient arcing during opening of the relay contacts.
A discharge resistor is also included preferably in series with the primary capacitor. This discharge resistor is optional. A second diode is also included positioned electrically in parallel with respect to the relay coil and also being electrically in parallel with respect to the first diode and is operatively oriented for current flow therethrough in order to suppress conductive power spiking through the relay coil.
The second solid state circuit means preferably includes a main solid state switching member which includes preferably a main triac positioned electrically in parallel with respect to the relay contacts in order to eliminate transient current arcing across the relay contacts when opening and closing thereof responsive to the main solid state switching device being operative. A switch firing resistor is also included electrically connected to the main solid state switching means to be powered simultaneously therewith.
The electromagnetic coupling means is preferably operative to provide electrical communication from the first solid state circuit to the second solid state circuit to selectively cause powering of the second solid state circuit responsive to activation of the first solid state circuit. The electromagnetic coupling device is preferably optically controlled and is electronically in parallel with respect to the primary capacitor means to facilitate operation thereof for a limited period of time responsive to discharge of the primary capacitor immediately after de-powering of the relay coil. The preferred configuration of the electromagnetic coupling means includes a light emitting diode positioned in series with the first diode and the current limiting resistor of the first solid state circuit to facilitate electromagnetic coupling between the first solid state circuit and the second solid state circuit. Also an optically activated solid state switching device such as an optotriac is located proximate to the light emitting diode and is included electrically in communication with respect to the main solid state switching means and is operative to activate the main solid state switching device responsive to activation of the light emitting diode. Thus, activation of the light emitting diode will turn on the optotriac which will communicate to a main triac located in the second solid state circuit such that conducting through the solid state switching apparatus across the relay contacts will occur.
An AC powering circuit means are also included electrically in communication with an AC load means for selectively supplying AC power thereto responsive to closing of the relay contacts or turning on of the solid state shunting switch.
It is an object of the relay circuit of the present invention to control the application of AC power to a load by suppression of transient arcing across the relay contacts wherein current flow through relay mechanical relay contacts immediately prior to closing and immediately after the initiation of opening is prevented.
It is an object of the relay circuit of the present invention to control the application of AC power to a load by suppression of transient arcing across the relay contacts wherein maintenance costs for refinishing or replacing relays is minimized.
It is an object of the relay circuit of the present invention to control the application of AC power to a load by suppression of transient arcing across the relay contacts wherein down time of mechanical apparatus is minimized.
It is an object of the relay circuit of the present invention to control the application of AC power to a load by suppression of transient arcing across the relay contacts wherein a relatively inexpensive solid state circuit can be used for suppression of transient arcing.
It is an object of the relay circuit of the present invention to control the application of AC power to a load by suppression of transient arcing across the relay contacts wherein the transmitting characteristics of mechanical contacts and solid state switching devices are coordinated to achieve a long lasting and effectively operating relay circuit means.
It is an object of the relay circuit of the present invention to control the application of AC power to a load by suppression of transient arcing across the relay contacts wherein the use of relatively expensive heat sinks and other heat dissipation devices is avoided.
It is an object of the relay circuit of the present invention to control the application of AC power to a load by suppression of transient arcing across the relay contacts wherein the surface condition of mechanical contacts of a relay coil can be maintained for vastly higher numbers of operations.
It is an object of the relay circuit of the present invention to control the application of AC power to a load by suppression of transient arcing across the relay contacts wherein usage is possible with either an AC or DC relay coil.
It is an object of the relay circuit of the present invention to control the application of AC power to a load by suppression of transient arcing across the relay contacts wherein unwanted transient arcing across relay contacts is achieved even during conditions of mechanical contact bounce.